The present invention relates to a heave resistant, deepwater platform supporting structure known as a "spar." More particularly, the present invention relates a deepwater catenary riser system suitable for deployment with such spars.
Efforts to economically develop offshore oil and gas fields in ever deeper water create many unique engineering challenges. One of these challenges is providing a suitable surface accessible structure. Spars provide a promising answer for meeting these challenges. Spar designs provide a heave resistant, floating structure characterized by an elongated, vertically disposed hull, having a very deep draft. Most often this hull is cylindrical, buoyant at the top and with ballast at the base. The hull is anchored to the ocean floor through risers, tethers, and/or mooring lines.
Vertical access production risers can connect production facilities on the platform to wells on the seafloor therebeneath. The production facilities receive and initially process the well fluids which are then sent into a subsea pipeline network through an export riser. While the ability to service the wells through a vertical riser is served by the production risers, these export lines derive no analogous benefit and it is desirable to avoid the complications required for motion compensated support attendant such vertical deployment. For this reason, export riser requirements are often addressed with deepwater steel catenary risers that may be supported directly by the platform.
Access to the catenary risers directly at the moonpool would be desirable to facilitate an officiant layout for processing facilities and bringing the risers onto the platform through the moonpool would serve to protect the risers from possible collision damage with service vessels. However, the very deep draft of the spar inhibits deploying the catenary risers through a central moonpool. Catenary risers may also be deployed for import risers connecting the spar to remote or satellite wells.
Thus, there is a clear need for catenary riser system suitable for deployment in a spar type offshore structure. Further there is a need for such a catenary riser system that is compatible with deploying vertical access production wells and/or drilling risers from the spar platform.